1. Field of the Invention
The present invention relates to a dispersion compensator and a dispersion-compensating module employing the dispersion compensator.
2. Description of Related Art
For high-speed and large-capacity optical communications, a dispersion compensation technique is inevitably required to reduce degradation in transmission caused by dispersion accumulated over the optical fiber transmission line. Typically, such a dispersion compensation technique employs dispersion compensating fibers.
Incidentally, it is necessary to compensate for different amounts of dispersion according to wavelength in wavelength division multiplexing communications in which a plurality of different wavelengths of light are multiplexed. This presented such a problem that dispersion compensation in the optical communication system required a dispersion-compensating fiber of length several to tens of kilometers for each wavelength, thereby increasing the size of the system.
In this case, it is conceivable to provide, on an optical transmission path for each wavelength, a dispersion-compensating module comprising a circulator and a fiber Bragg grating (FBG), yet narrow in bandwidth, for compensating for dispersion. However, this method has a drawback that an increase in number of wavelengths will correspondingly increase the number of dispersion-compensating modules, leading to an increase in cost for dispersion compensation since the circulator is expensive. In addition, there was another problem that it was necessary to connect an optical transmission path to each of said circulators for each wavelength in the dispersion-compensating module, which makes the connection complicated.
An object of the present invention is to provide a dispersion compensator which can be used for dispersion compensation in a wavelength division multiplexing communication system and which can make the optical communication system less in size than does the conventional dispersion compensation fiber. Another object of the present invention is to provide a dispersion-compensating module which facilitates the connection to the component parts.
To achieve the aforementioned objects, the dispersion compensator according to the present invention employs an arrayed waveguide grating comprising at least one input waveguide, a first slab waveguide, an arrayed waveguide having a plurality of channel waveguides, a second slab waveguide, and a plurality of output waveguides are formed on a substrate. The dispersion compensator is configured such that Bragg gratings, each having a dispersion compensating function, are formed on the plurality of output waveguides of the arrayed waveguide grating.
Furthermore, to achieve the aforementioned objects, the dispersion compensator according to the present invention is configured such that planar waveguides provided with a predetermined number of Bragg gratings having a dispersion compensating function are connected to output waveguides of an arrayed waveguide grating.
The planar waveguides are preferably a plurality of waveguides formed on a substrate.
Moreover, the substrate is preferably formed of silicon or glass.
Furthermore, to achieve the aforementioned objects, the dispersion-compensating module according to the present invention comprises a circulator having an input port, an output port, and a connecting port. The dispersion-compensating module also comprises aforesaid dispersion compensator connected to the connecting port of the circulator, and an optical demultiplexer comprising an arrayed waveguide grating connected to the output port of the circulator.
According to the present invention, it is made possible to provide a dispersion compensator which can be used for dispersion compensation in a wavelength division multiplexing communication system and which can make the optical communication system less in size than does the conventional dispersion compensation fiber. It is also made possible to provide a dispersion-compensating module which facilitates the connection to the component parts.
These and other objects, features and advantages of the present invention will become clear from the following detailed description with reference to the accompanying drawings.